1. Field of the Invention
This invention relates to the melting of vitrifiable materials and in particular a process and an electric melting furnace for melting glass obtained by the heat released by the Joule effect.
2. Description of the Related Art
Among the different known types of electric furnaces for melting glass, melting furnaces called cold furnaces or cupola furnaces are furnaces in which the solid composition of vitrifiable materials, supplied from above, forms an upper layer that completely covers the bath of molten glass. The melted glass is removed at the bottom part of the furnace by a throat and then passes into the following cell, which can be a refining cell, then to conditioning process.
One of the problems encountered in this type of furnace, especially when it operates at elevated glass temperatures, on the order of 1500.degree. C., is the rapid wear of the refractories defining the throat, and in particular of the refractories defining the upper part of the throat.
Indeed, despite the use of cooling systems limiting the attack on the refractories by glass at high temperature, these refractories must generally be replaced more quickly than other refractory elements of the furnace. Such a replacement requires stopping the furnace or, at least when possible, a repair while it is hot, involving stopping production.
In addition, the refractory parts constituting the crown of the throat generally have limited maximum dimensions such that the cross section of the throat itself has limited dimensions. The result, for a furnace that uses such a throat as a discharge opening for removing the melted glass, is a limited load capacity generally not exceeding 200 tons/day.